Half-bridge topology can be a good candidate for high power density direct current-direct current (DC—DC) conversion especially in those applications that use Point-Of-Load DC—DC converters for present and future generation of integrated circuits. This is because of several reasons including structure simplicity, lower number of switches, lower isolation transformer primary side turns since half of the input voltage is applied to the transformer windings, and possibility to achieve soft-switching with the appropriate control. There are two main conventional control schemes used in half-bridge topology. One is the conventional symmetric phase width modulated (PWM) control and the other is the asymmetric (complimentary) control where two driving signals are complimentarily generated.
The switching frequency continues to increase mainly to reduce the size and cost of passive components and to improve the dynamic performance. Hence, soft-switching techniques becomes more desirable in order to reduce the increased switching losses and switches body diode reverse recovery losses at these increased switching frequencies.
When the conventional symmetric control is used for half-bridge, its two switches operate at hard-switching, while when the asymmetric control is used, the two half-bridge switches operate at soft-switching, but unfortunately, causing asymmetric stresses on the converter components which is not desirable especially for wide input voltage range, say 35V˜75V or 300V˜400V. Moreover, the DC gain is not linear which degrades the converter performance.